Infrared telescopes need to be very cold (often below 10 K) to be effective. So do a few other miscellaneous things, including superconductors, if we ever use them in space for e.g. mass drivers or radiation shielding. When it's launched, JWST will have a 500W-550W four-stage cooling system that manages to reject a measly 76mW at 6.2 K — roughly a 7000 to 1 input power to useful cooling load ratio. However, the Zeeman slower seems tailor-made for this, since it cools only with radiated heat, can cool down to the required temperature range, and is already sometimes used instead of that same basic refrigeration design (Joule-Thomson etc) in Earth-bound labs, where there's convection and conduction to dump the extra heat more efficiently than via radiation alone. Given this, are there any obstacles to Zeeman slowers being seriously considered for cold-instrument mission design in the near future?

(This is a more focused version of a similar question I recently asked, about general systems cooling.)


1 Answer 1


To make an answer out of my comment:

This paper talks about a flow of about 20 billion Caesium atoms per second and characterizes that as a "high flow". So let us use that as an example...

20*109 atom/s, cooled, say 273 Kelvin (from 0°C to 0K), at 32.2 J/(mol K) is a heat flow of...

29*10-6 mW.

In other words: not even one part in a million compared to the JWST cooling system, and that is with extreme assumptions regarding the temperature of what this system is cooling.

So just forget it... the heat flow is much too small.

  • $\begingroup$ That's a fair calculation, although given that the paper was state of the art 17 years ago, and slowers are only about 30 years old, it's hard to be sure how much more progress has been made since then. I would also appreciate an answer that explains why slowers are used at all if their heat flow is so very low compared to conventional cooling systems, as a sanity check. $\endgroup$ Mar 29, 2016 at 17:57
  • $\begingroup$ @NathanTuggy Well the general answer to the question "Why is something so hugely inefficient used instead of other similar systems?" is always "Because the hugely inefficient system does something special that the other systems do not", in other words it is efficient, for a specific application. I believe Zeeman coolers are used because they allow temperaturs that are not achievable with other coolers. $\endgroup$
    – MichaelK
    Mar 31, 2016 at 7:05
  • $\begingroup$ That sounds plausible, but given the substantial temperature overlap between conventional cooling and Zeeman slowers, it can't be just that... or else the slowers would only be used for the last few degrees, just like most laser cooling systems. The paper linked seems to start with temperatures around 70-100 K, which is far above the minimum the JWST's systems go to. $\endgroup$ Mar 31, 2016 at 18:27
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    $\begingroup$ @NathanTuggy I don't know why this is so important to you but let me assure you: no, you have — in all reasonable likelihood — not found some cool innovation in spacecraft cooling that NASA and everyone else just happened to overlook. Just drop it... or call the nearest university physics institution and ask them about the practical details about Zeeman slowers instead of going on SE and expecting people to do get that info for you. $\endgroup$
    – MichaelK
    Mar 31, 2016 at 18:32
  • $\begingroup$ It's important to me because I want to know why it doesn't work. An answer that says "well, for reasons that are doubtless good and sufficient" is not good for SE, or indeed anywhere except kindergarten. And the point of SE is to make it so everyone with the same question (all four of us, presumably) don't have to independently go through all the same difficult, tedious, and/or expensive research to find the answer. If you really think this is a pointless question, go ahead and downvote. Otherwise, maybe someone else will have the inside scoop. $\endgroup$ Mar 31, 2016 at 18:44

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